What is Highway Alignment?
The position or layout of the centerline of the highway on the ground is called highway alignment. The horizontal alignment includes the horizontal paths and horizontal curves vertical aluminum includes gradient and vertical curves.
The highway should align carefully as improper alignment should result.
This all increases in
- Construction cost.
- Maintenance cost.
- Vertical operation cost.
- Accident rates.
The ideal requirement of Highway Alignment.
Short
Alignment should be short. That is the minimum traveling distance.
Easy
The alignment should be easy to construct and maintain and easy for vehicle operation with easy curves and gradients.
Safe
Alignment should be safe for construction and maintenance. It should be safe for traffic operation with a geometric design.
Economic
Alignment could be considered economical only if the total cost including initial cost maintenance cost and vehicle operating cost is the lowest.
Factor controlling Highway Alignment
- Geometric consideration
- Obligatory points
- Traffic considerate
- Economic considerate
- Other considerate.
Obligatory point
Points through which highway Alignment should pass:
- Along with hill parts.
- Suit the proper location of the bridge.
- Connect intermediate town.
- Connect industrial zone.
- Avoiding the intermediate area.
Points through which highway should not pass.
- Waterlogged area marshy land.
- Historical and archaeologically important places.
- Restricted zone for defense national security.
- Densely populated area.
- Costly structural element.
Traffic
The new road should align keeping in view the desired line, traffic flow pattern, and future trends.
Geometric design
Geometric design such as the gradient radius of the curve, and sight distance also governs the final alignment of the highway.
Economy: B/C>1
In working out the economics the initial cost of maintenance and vehicle operation cost should be taken into account. The initial cost can decrease if high embankment and deep cutting are avoided and the alignment is chosen in a manner to balance the cutting and filling.
Other factors
Various factors that control highway alignment are drainage consideration, hydrological, factors, surface water level, seepage flow, high flood level, etc.
Engineering Survey for Highway Alignment
In this survey, the different methods include. Which will be discussed in these articles.
- Map study
- Reconnaissance (recce)
- Preliminary survey
- Final location and details survey
These are the methods for highway alignment surveys. Which method is important in the highway alignment selection? So let’s begin with details about it.
Map study
If the topographic map is available, it is possible to fix the routes of the road.
The main feature like rivers, hills, valley, etc. is also shown on their map.
By the study of such maps, it is possible to have an idea of several possible alternate routes so that further details of these may be studied later on site. The possible different alignments can be selected on the topo map.
- Alignment avoiding valley pond or lake.
- When the road has to cross a row of hills possible the cross through a mountain pass.
- Approximate location of bridge site for crossing rivers avoiding bends of rivers if any.
- In the map study, the alternate routes of the road can be fixed. It gives rough guidance of the routes to be further surveyed in the field.
Recent
- All the possible details that are not available in the map study are collected and noted down.
- The details collected are below:
- Valley, ponds, marshy land, and other permanent structures along the route are not available on the map.
- Approximate values of the gradient, length of the gradient, and curve radius of alignment.
- No and type of cross drainage structure, maximum flood level groundwater level.
- Soil type along the alignment.
- Source of construction material, water, and location of stone quarries.
- As a result of the reconnaissance survey, a few alternative alignments may be chosen for future study.
Preliminary survey.
The main objective of the preliminary survey is
- To collect the necessary physical information and details of topography drainage and soil of various alternative alignments.
- Compare different proposals because of the requirement of good alignment.
- Estimate the quantity of earthwork and work out the cost of alternate alignment.
- Finalize the best alignment from all the considerations.
- The survey was carried out by the following method.